25 



■0H£ 



'OH- 



Al 



+ SQ 



2- 



4- 



_^ 



v 



Al 



OH. 



A 



o+ 



OH. 



or 



-OH 



■90^ 



A 



•SO, 



OH. 



'SO 



4 J 



+ OH' 



OH 



Al' 



OH 2 



O. 



O" 



^ 

 X 



o 



o 



OH2 



OH" 



Fig. 1. Raian's (1978) proposed mechanism of sulfate adsorption. 



